846
Macromolecules 1993,26, 846-848
Synthesis of a New Side-Chain Liquid Crystalline Polymer with a Polynorbornene Main Chain by Ring-Opening Metathesis Polymerization Sung-Hyun Kim, Hyung-Jong Lee, Sung-Eo Jin, Hyun-Nam Cho,+and Sam-KwonChoi' Department of Chemistry, Korea Advanced Institute of Science and Technology, 373-1 Kusung-Dong Yusung-Gu, Daeijon, Korea Received June 19,1992 Revised Manuscript Received October 16,1992
Introduction In recent yeara considerableeffort has been directed to the synthesis of novel side-chain liquid crystalline (LC) polymers because of a variety of applications, especially in the field of e1ectrooptics.l Side-chainliquid crystallinity generally requires a molecular structure in which a flexible polymer chain, or flexible connector group between the mesogen and backbone,providessufficient conformational freedom to allow the rigid mesogenic units to form stacks or organized domain~.~>3 The types of polymer backbones used for the synthesis of side-chain LC polymers have been limited to polysilo~anes,4~~ p ~ l y a c r y l a t e sand ~~~ polymethacrylate~.~.~ There are only a few examples in which other main-chain structures like polyolefin,"Jpoly(vinyl ether),11J2polyphosphazene,13J4or polyoxetane15 are used. We have been interested in the effects of the structure of the main chain, the length of the spacers, and the structure of the mesogenic group on the liquid crystalline phase exhibited. In our previous work we reported a novel thermotropic side-chain LC polymer with electrical conductivity synthesized by transition metal catalyst aystems.16 In this paper, we report a new example of an LC polymer that has a polynorbornene main chain and a methoxy-substituted biphenyl mesogenic group. Experimental Section Monomer. The monomer 5-([[5[(4-methoxybipheny1-4'-yl)oxylpentyl]oxy]methyl)-2-norbornenewas synthesized by the reaction of the 4-methoxy-4'-hydroxybiphenylmesogenic group with an exo,endo mixture of 5-((5-bromopentoxy)methyl)-2norbornene in the presence of KzC03 using DMF as solvent: yield 86%.
The structure of the product was identified by elemental analysis, MS, IR, and 'H NMR, and 13CNMR. Elemental anal. Calcd for C&3& 79.56; H, 8.22. Found: C, 79.38; H, 8.03. M S m/e 392 (parent), 200 (base). I R 3057 (HC=, vinylic), 1568 (CH-CH, vinylic), 1606, 1475 (C==C, aromatic), 824, 807 (aromatic para substitution), 717 cm-I (cisarrangement of double bond). lH NMR (CDC13): 6 (ppm) 1.2-1.8 [m, 10 H, (CH& CHJ, [2.25 (m), 2.71 (br d), 2.83 (br d), 2.94 (t), 3.06 (dd), 3 H, the nonolefinic norbornene protons], 3.3-3.4 (m, 4 H, CHzOCHz), 3.76 (s,3 H, OCHz), 3.92 (t, 2 H, CHZOAr), [5.85 (dd),6.05 (dd),
* To whom correspondence should be addressed.
'
Polymer Materials Laboratory, Korea Institute of Science and Technology, P.O. Box 131, Cheangyangri, Seoul, Korea. 0024-9297/93/2226-0846$04.00/0
olefinic methine of the endo isomer], 6.01 (m, olefinic methine of the exo isomer), 6.87 (dd, 4 H, aromatic), 7.39 (dd, 4 H, aromatic). I3CNMR (CDC13): 6 (ppm) 55.2 (OCH3),132.4 (C(2)), 139.6 (C(3)), 158.1 and 158.6 (alkoxy-substituted 4,4'-aromatic carbons). The ratio of endo to exo isomers calculated from the ratio of the corresponding olefinic resonances is 7921. Polymer. Catalyst preparation and polymerization were carried out under a dry-nitrogen atmosphere. Transition metal halides and organometallic compound8 were dissolved in each solvent to make a 0.2 M solution before use. A typical polymerization procedure was as follows: solvent, catalyst solution, and when needed, cocatalyst solution were injected into a 20-mL ampule equipped with a rubber septum in the order given. When the cocatalyst was used, the catalyst system was aged at 50 "C for 15 min. Finally, the monomer solution was injected into a polymerization ampule. After the reaction mixture was allowed to react at 60 "C for 24 h, polymerization was terminated by adding a small amount of methanol. The reaction mixture was dropped into methanol with rapid stirring, and the precipitate separated from the solution and was washed twice withmethanol. The polymer was filtered and dried under vacuum at 40 O C for 2 days. The polymer yield was determined by gravimetry.
Catalyst : Mock, WCl,, WC14(OAr)2 Cocatalyst : EL41C12. Et&
PbEt,
Results and Discussion In Table I the results for the ring-opening metathesis polymerization of the monomerby various catalystsystems are listed. Ma15 and WC& alone give very low polymer yields. However, when EtAlC12 or E t A was used as cocatalyst, the polymer yield increased. When the mole ratio of monomer to catalyst was relatively low, the yield wasimproved. The WC&(0-2,6-CsH&, X = Ph)zcatalyst system,17which is well known to have a good tolerating propertyto polar functionalgroupsin metathesisreactions, was found to be effective. In this system, it was found that PbEt4 is an excellent cocatalyst. It was shown that the resulting polymerswith relatively high number-average molecular weights exhibit good solubility in common organic solvents such as THF, chloroform, toluene, DMF, etc. However, in certain catalyst system (nos. 6 and 7 in Table I), we obtained high molecular weight polymers which were just swelled in the above organic solvents. Careful lH NMR, 13C NMR, and IR analyses were carried out to prove the chemicalstructure of the polymer. As the polymerization proceeded (Figure 3), the vinylic proton peaks at 5.85 and 6.04 ppm disappeared. The lH NMR spectrum of the polymer shows new vinyl protons as broad signals between 5.15 and 5.26 ppm in the ratio of approximately 64. These broad signals correspond to the vinyl protons of the cis and trans double bond of the ring-opened polymer, respectively. One of the main differences between the IR of the monomer and that of the polymer is that there is a strong band at 719 cm-l in the monomer but a very weak band at 710 cm-' and a broad band at 970 cm-l in the polymer. The strong band about 719cm-l is due to the cis arrangementabout a double bond in which the = C H bond can undergo an out-ofplane bending vibration,while a trans double bond usually absorbsnear 970cm-l in such a vibration mode. The above IR information also supporta that the ring-opened polynor0 1993 American Chemical Society
Macromokcules, Vol. 26,No.4, 1993
Notes a47 Table I
Polvmeriution of. the Monomer with Vnrionn Transition Metal Catalvntn
6 7
0.5
50
82
8
MoClsEtAlCll(1:4) 50 0.5 58 8 8 Mock 50 0.5 trace 9 wcls 50 0.5 trace .A mixtare of catalyst and cocatalyst in chlombsrusne was aged at 50 OC for 15 min. before use as catalyd. Monomer to catalyst mole ratio. Initial monomer concentration. Methanol-insoluble polymer. e Values were obtained hy GPC d y s k with polystyrene standard calibration. /Polymerization procedureby this catalyst systemproceededasfollow: l ( r ' l O ~ m o l o f W C 4 ~ 0 - 2 , 6 ~ j XX~ .= Ph)nwm placed in an ampule in such a way that the catalyst concentration WBS 0.02 M. The solution WBB heated to 80 'C and P h E t was syringed in. The resulting catalyst mixture WBS then transferred to another ampule with a cannula in which the monomer WBB kept at the reaction temperature. The ampule was maintained at M) OC for 4 h. 8 Hiah molecular weight polymers which were swelled in THF, toluene, chlorobenzene. DMF, chloroform, etc.
*
2.0
I
A
I.4
02
-50
0
50
IO0
I50
*rempemture(w (B)
Figure 1. DSC tram of the monomer (A) and the polymer (B) (scanning rate = 10 OC/min) (sample: no. 3 in Table I).
bornene main chain has both cis and trans double bonds. In the IaC NMR spedroecopy, the monomer gave vinylic w b o n peaks at 132.4and 136.9ppm. On the other hand, the polymer did not show thew peaka, instead, the various vinylic carbon peaks of the ring-opened polymer backbone appeared between 130 and 135 ppm. The olefinic carbon chemid shift depends not only upon the nature of the double bond (cis or trans) hut also on the arrangements of the two repeat units from which the double bond is derived, Le., HH, HT (TH), or 'IT. It should be noted that in the polymerization of substituted norbornens there are two types of propagatingspecies,represented by 1and 2.
(B)
Figure 2. Microphotographs of the monomer (A) taken at €4 'C and the polymer (B) taken a t 70 OC (sample: no. 4 in Table I). [Mtl =CH
P
CH=CHh
1
IMtl=CH
CH=CHFn
2
1can add monomer to give HH or HT structum while 2 can add monomer to give TH or 'IT StNCturea (H= head,T = tail). Therefore,owingtotheabovetworeasons, such variousvinylic carbon peaksappeared in the IaC NMR spectrum of the polymer. Figure 1A showsthe DSC tramobtainedfor consemtive
heating and cooling cyclea on the monomer. The large
848 Notes
Macromolecules, Vol. 26, No. 4,1993
of the DSC curves, a prominent endothermic transition (isotropization)is found the correspondingenthalpy AHm is 3.96W g . Thisrelatively large enthalpyof isotropization is attributable to the tranaition from the highly ordered state to the isotropic liquid state. Figure 2B is a microphotograph of the polymer taken at 70 "C. On the cooling scan from the isotropic state, batonneta began to appear on the dark background at 71 OC, growing gradually, and finally a fanlike texture was observed. The mesophase found for the polymer is supposed to be a smectic mesophase because of both the large enthalpy of isotropization and the batonnets and fanlike textures observed by polarized optical microscopy. In addition to research on the effect of the length of the spacers and the structure of the mesogenic group on the liquid crystalline phase exhibited, studies to increaee the types of main chains are in progress. Acknowledgment. We gratefully acknowledge the support of this work by the Korea Science and Engineering Foundation. References and Notes (1) (a) Finkelmann, H.; Keichle, U.;Rehage, G. Mol. Cryst. Liq. Cryst. 1983,94,3453. (b) Colea, H.J.; Simon, R. In Recent Advances in Liquid Crystalline Polymers; Chapoy, L. L.,Ed.;
Figure 3. lH NMR spectraofthe monomer (A) and the polymer (B)(sample: no. 4 in Table I).
transition peak at 67 O C on the cooling scan is thought to be due to the isotropic liquid-smectic mesophase transition. The transition enthalpy from the isotropic phase to the LC phase is 9.96 cal/g on the cooling scan. On the second h~scan,mdtiplemeltingendotbetmicpeaks
which ware not castected during the cooling mm were observed M e e n 68 and 97 OC, which are attributed to the endo/exo isomeric mixture. Figure 2A shows the photomicrographic properties of the LC state. of the monomer which indiatd that* first peak and the last peakontheheatiag~wereduetoasolid-smecticliquid crystal transition and a camplete isotzopiaation, respectively. Figure 1B preeente the oooling and the second heating DSC traces of the polymer. In the heating part
Elsevier Applied Science: New York, 1985; Chapter 22. (2) Finkelmann, H.; Ringedorf, H.; Wendroff, J. H. Makromol. Chem. 1978,179,273. (3) Finkelmann, H.; Happ, M.;Portugall, M.;Ringedorf, H. Makromol. Chem. 1978,179,2541. (4) Skibaev, V. P.; Plate, N. A. Adv. Polym. Sci. 1984,60/61,173. (5) Finkelmann, H.; Rehage, G. Makromol. Chem., Rapid Commun. 1980,1,31. (6) Portugall, M.;Rigsdorf,H.;Zentel,R.Makromol. Chem. 1982, 183,2311. (7) Decobert, G.; Soyer, F.; Dubois, J. C. Polym. Bull. 1985, 14, 179. (8) Finkelmann, H.; Rehage, G. Ado. Polym. Sci. 1984,60/61,99. (9) Zentel, R.;Ringedorf, H. Makromol. Chem., Rapid Commun. 1984, 5, 393. (10) Mallon, J. J.; Kantor, S. W. Macromolecules 1989,22,2070. (11) Sagane, T.; Lenz, R. W.Polym. J. 1988,20,923. (12) Percec, V.; Lee,M. Macromolecules 1991,24,1017. (13) Singler, R. E.; Willingham, R. A; Lenz,€2. W.; Furukawa, A.; Finkelmann, H. Macromolecules 1987,20,1728. (14) Allcock, H. R.;Kim, C. Macromolecules 1990,23, 3881. (15) Kawakami,Y.; Takahashi,K.; Hibino, H. Macromolecules 1991, 24, 4531. (16) Jin, S.H.; Kim, S. H.; Cho, H. N.; Choi, S. K. Macromolecules 1991,24,6050. (17) Quignard, F.; Leconte, M.; Basset, J. M.Znorg. Chem. 1987, 26, 4272.
